At least 44 people were killed and hundreds more injured by a series of enormous explosions at a hazardous materials warehouse in the northeastern Chinese port city of Tianjin late Wednesday.

Pictures and videos showed gigantic plumes of fire and a mushroom cloud that dwarfed nearby high-rise buildings and sent a massive shockwave that rattled residents several kilometers from the blast site.

A man checks his mobile phone near shipping containers that were overturned by the force of two huge explosions in the Binhai district of Tianjin, China, August 13, 2015.

​Hundreds of firefighters are trying to contain the blaze, but their efforts have been complicated by "complex conditions" at the site, according to Xinhua. Several reports have suggested firefighters have had to suspend their efforts until it can be determined there are no more dangerous chemicals present.

State media say at least 32 people remain in critical condition after the explosions. At least 400 people were injured.

The first explosion, which took place just after 11:30 a.m. local time, was equal to three tons of TNT, according to the China Earthquake Networks Center. A second blast 30 seconds later was equal to 21 tons of TNT, it said.

The explosion blew out windows and rattled residents up to several kilometers away.

"There was one gust of wind, an unnaturally large gust, and then a really really large gust followed by a bit of a shake," Drew Chovanec, an English teacher who lives about 5 kilometers (3 miles) from the blast, told VOA. "We saw the plume of smoke and the light pretty clearly afterwards."

There are no indications about what caused the explosion, which state media say occurred at a warehouse owned by Rui Hai International Logistics. Local authorities said the company's senior management have been taken into custody.

Tianjin is a port city in northeastern China, about 150 kilometers (93 miles) southeast of Beijing, and is home to more than 7 million people. It is China's fourth largest city.